feat: add tenant and user management with migrations, handlers, and tests

- Implemented tenant and user management features including:
  - Tenant creation and management with associated migrations.
  - User creation and management with associated migrations.
  - Tenant membership management with associated migrations.
  - Platform user roles management with associated migrations.
  - Quota management with associated migrations.
  - Article and template management with associated migrations.
- Added HTTP handlers for templates and workspaces.
- Created tests for protected and public routes.
- Introduced a script to check tenant scope in SQL queries.
- Documented task plan for backend completion and frontend foundation.

server/internal/shared/response/errors.go

@@ -0,0 +1,35 @@
+package response
+
+import "net/http"
+
+func ErrBadRequest(code int, message, detail string) *AppError {
+	return &AppError{HTTPStatus: http.StatusBadRequest, Code: code, Message: message, Detail: detail}
+}
+
+func ErrUnauthorized(code int, message, detail string) *AppError {
+	return &AppError{HTTPStatus: http.StatusUnauthorized, Code: code, Message: message, Detail: detail}
+}
+
+func ErrForbidden(code int, message, detail string) *AppError {
+	return &AppError{HTTPStatus: http.StatusForbidden, Code: code, Message: message, Detail: detail}
+}
+
+func ErrNotFound(code int, message, detail string) *AppError {
+	return &AppError{HTTPStatus: http.StatusNotFound, Code: code, Message: message, Detail: detail}
+}
+
+func ErrConflict(code int, message, detail string) *AppError {
+	return &AppError{HTTPStatus: http.StatusConflict, Code: code, Message: message, Detail: detail}
+}
+
+func ErrTooManyRequests(code int, message, detail string) *AppError {
+	return &AppError{HTTPStatus: http.StatusTooManyRequests, Code: code, Message: message, Detail: detail}
+}
+
+func ErrInternal(code int, message, detail string) *AppError {
+	return &AppError{HTTPStatus: http.StatusInternalServerError, Code: code, Message: message, Detail: detail}
+}
+
+func ErrServiceUnavailable(code int, message, detail string) *AppError {
+	return &AppError{HTTPStatus: http.StatusServiceUnavailable, Code: code, Message: message, Detail: detail}
+}